Tests: Refactor tests with better names, etc.

The basic tests now run on Windows correctly without needing to manually
copy any files -- the executables are output in the same location as the
necessary DLLs. However, tests that require *.pyd files (all code in the
Mod subdirectory, basically) still do not work on Windows as the test
executables cannot find those files. This is a work in progress.

tests/src/Mod/Start/App/CMakeLists.txt

@@ -1,8 +1,6 @@
-target_sources(
-    Start_tests_run
-        PRIVATE
-            ${CMAKE_CURRENT_SOURCE_DIR}/FileUtilities.cpp
-            ${CMAKE_CURRENT_SOURCE_DIR}/ThumbnailSource.cpp
+add_executable(Start_tests_run
+        FileUtilities.cpp
+        ThumbnailSource.cpp
 )
 
 target_include_directories(

tests/src/Mod/Start/CMakeLists.txt

@@ -1,3 +1,4 @@
+add_subdirectory(App)
 
 target_include_directories(Start_tests_run PUBLIC
     ${Python3_INCLUDE_DIRS}
@@ -8,5 +9,3 @@ target_link_libraries(Start_tests_run
     ${Google_Tests_LIBS}
     Start
 )
-
-add_subdirectory(App)